The disclosure relates to a vehicle brake system with wheel slip control. Such a vehicle brake system is disclosed, for example, by DE 102010042534 A1.
This known vehicle brake system comprises a hydraulic unit with a brake master cylinder connected thereto and wheel brakes likewise connected thereto. The brake master cylinder can be actuated physically by the driver of the vehicle in order to supply brake pressure to the vehicle brake system. The brake pressure is delivered to the wheel brakes and is adjusted by control devices of the hydraulic unit to the wheel slip conditions prevailing at any given instant on the vehicle wheels associated with the wheel brakes. For this purpose, so-called pressure build-up valves and pressure reduction valves, which are in each case assigned in pairs to each wheel brake, are provided on the hydraulic unit. The pressure build-up valves control a flow of fluid to the wheel brakes should an increase in brake pressure be necessary, whilst the pressure reduction valves allow a discharge of fluid if the brake pressure on the wheel brake should be too high and the wheel threatens to lock.
For regulating the brake pressure an actuatable pressure generator, which is connected by its suction side to a return from the wheel brakes controlled by the pressure reduction valve, is furthermore provided on the hydraulic unit. Fluid is transported away from the wheel brakes via the pressure reduction valve. A delivery side of the pressure generator is connected to an inlet of the wheel brake controlled by the pressure build-up valve. For controlling the flow of fluid through the pressure generator the latter is fitted with a pump inlet valve on the suction side and with a pump discharge valve on the delivery side.
The brake master cylinder of the vehicle brake system is moreover connected to the delivery side of the pressure generator. Consequently, when the brake master cylinder is actuated the increased brake pressure acts on the delivery side of the pressure generator, thereby making it more difficult to start. This occurs particularly in ABS braking sequences, in which the brake pressure is generated by the driver and in which the pressure generator starts up in order to regulate the brake pressure. In order to allow the pressure generator to start up despite the prevailing counter-pressure, its drive is designed to afford commensurate power, but on the other hand is of relatively large and heavy construction.
New system functions, such as pedestrian safeguards, for example, exacerbate the problem explained above. They require an especially rapid build-up of brake pressure on the wheel brakes and assume that ever greater volumes of fluid can be fed to the wheel brakes in ever shorter times. An adaptation of the pressure generator designed to cater for this need means that the design performance of its drive has to be increased yet further, therefore once again making it larger and heavier. Compact dimensions and a low weight, however, are fundamental requirements in vehicle manufacturing.